In conventional internal combustion engines, a mixture of air and fuel is introduced into the engine, where it is compressed and then ignited. The burning gases expand, do work, and then are expelled from the engine. The actual amount of kinetic energy or mechanical work that is extracted from the internal combustion generally depends upon the thermal efficiency of the internal combustion engine. What is not extracted is expended as waste heat.
Thermal efficiency is the percentage of energy taken from the combustion which is actually converted to mechanical work. In a typical low compression engine, the thermal efficiency may be only about 26%. In a highly modified engine, such as a race engine, the thermal efficiency may be about 34%.
In a generic internal combustion engine, only 20% of the total energy available may be converted to useful energy. Of the remaining 80% of the total energy, approximately 38% may be lost through exhaust heat, 36% through water heating in the cooling system and 6% through motor friction.
There have been various schemes to capture energy from the exhaust gases and heated engine cooling water.
U.S. Pat. No. 4,439,999, Mori, et al., discloses an internal combustion engine and an absorption type refrigeration system which makes use of both the engine exhaust gas and the heated engine cooling water. The internal combustion engine and the absorption type refrigeration system are combined in such a manner that the exhaust gas of the internal combustion engine is utilized as the heat source for a first gaseous refrigerant generator having the highest operating temperature in the system, while heated engine cooling water is utilized as the heat source for another generator which operates at a temperature lower than the operating temperature of the first gaseous refrigerant generator.
U.S. Pat. No. 6,119,457 to Kawamura describes a heat exchange apparatus having high and low temperature heat exchangers comprising porous material provided in an exhaust passage from a ceramic engine in communication with a supercharger connected to the ceramic engine. The heat exchange apparatus comprises a high temperature heat exchanger having a steam passage provided in an exhaust gas passage through which an exhaust gas passes whereby steam is heated, and a low temperature heat exchanger provided in the portion of the exhaust gas passage on the downstream side of the high temperature heat exchanger which has a water passage for heating water by the exhaust gas. The ceramic engine has a steam turbine type supercharger provided with a steam turbine driven by the steam from the high temperature heat exchanges, a compressor, and a condenser which separates a fluid discharged from the steam turbine into water and low temperature steam. Pressurized air from the compressor is supplied to the combustion chamber, which presses down a piston to carry out compression work during an intake stroke. Thus, the supercharger is driven by the thermal energy recovered from an exhaust gas by the same heat exchanger apparatus.
An example of an energy recovery system is also disclosed in Japanese Patent Laid-Open No. 179972/1993. This energy recovery system has an energy recovery unit provided with a first turbine installed in an exhaust passage and a generator operated by the first turbine, a turbocharger provided with a second turbine connected to an outlet-side passage of the first turbine and a supercharging compressor operated by the second turbine, and a waste gate provided in the outlet-side passage of the first turbine. The energy recovering operation is carried out by the energy recovery unit when the temperature of the exhaust gas is high.
Exhaust gas energy from an internal combustion engine may also be used to provide a heated water source, for example, while the mechanical power of the engine may be used simultaneously to generate electricity. In Japanese Patent Laid-Open No. 33707/1994, there is disclosed a system making use of exhaust gas energy from a turbocharger attached to a heat insulation type gas engine to produce steam that is used to drive a steam turbine so as to produce electric energy and heated water. A turbocharger is driven by the exhaust gas energy from the heat insulating gas engine, and the generator/energy recovery unit is driven by the exhaust gas energy from the turbocharger. The thermal energy of the exhaust gas directed to the energy recovery unit is converted into steam by a first heat exchanger, and recovered as electric energy by driving a steam turbine. Heated water is generated by the high-temperature steam from the steam turbine by an operation of a second heat exchanger, and utilized as a hot water supply source.
In U.S. Pat. No. 4,803,958 to Erickson, there is disclosed an open-cycle absorption apparatus for compressing steam from a low pressure to a higher pressure. The apparatus is used for upgrading low-temperature jacket-cooling heat from an internal combustion engine to useful pressure steam. A simple heat-exchange apparatus is involved, using the extra temperature availability of the hot exhaust gas as the driving medium.
There have recently been higher efficiency vehicles powered using hybrid concepts that involve internal combustion engines in combination with an electric generator that powers an electric motor. The generator utilizes some of the kinetic energy that would otherwise be converted into heat by friction in the vehicle's braking system. While systems such as described above in combination with such hybrid systems may further improve energy storage in such cars, the loss of energy through the emission system would remain high. What is needed is a system that would convert a significant percentage of the power lost as heat to electrical power and create a more efficient hybrid vehicle.